Four turtles fall into the sewers of New York City and are befriended by Hamato Yoshi, a Japanese man who lives in this subterranean refuge. One day Yoshi encounters a strange green glow of sewer sludge, which transforms him into a giant mutant rat named Splinter and the four turtles into humanoid creatures. Master Splinter dedicates his time to teaching the skills of the ninja to the turtles, who have become superpowerful from the radioactive waste floating in the sludge, and thus the Teenage Mutant Ninja Turtles (TMNT) are born.

For thirteen years, they protected the Earth from within their headquarters, the Hall of Justice. If they had kept their title the same, ABC and Hanna-Barbera's group of superheroes would have been among the longest-running animated series in history, but even though they always got along, the Super Friends got new series titles on a regular basis. The core team always remained Superman, Batman, Wonder Woman, Robin, and Aquaman, although multiple other heroes and sidekicks often joined them for adventures.

Joseph Campbell, author of The Hero with a Thousand Faces (1949) and respected interpreter of heroic lore, noted that heroes often have helpers along their mythic journey. Though the traditional sidekick has often fulfilled this role through comics history, the superpet has occasionally proved to be a hero's best friend in perilous circumstances.